The present invention relates to a focus condition indicating system for use in a camera for indicating an in-focused condition of an objective lens.
When taking a photograph, it is necessary to adjust the position of the focusing element or of the entire camera objective lens by shifting the element or the whole lens along its optical axis in a direction away from or towards a focal plane, i.e., a film surface, so as to properly focus the image of an object to be photographed on the film surface.
When the image, as viewed through the viewfinder, is found to be out of focus, it is difficult to tell at the very beginning of the adjustment to which direction should the lens be shifted, and it often takes a long period of time before the lens is shifted to the proper focus position.
In consideration of such an inconvenience, there has been proposed a visual indicator having a signal producing means for producing a signal that indicates the side on which the lens is located from its proper focus position, and a display means including a lamp or meter capable of showing in the field of a viewfinder the direction to which the lens should be shifted to bring the lens into the proper focus position. This type of indicator is disclosed in the Japanese Patent Application of Werner Holle, laid open to the public on Apr. 19, 1977 by laid-open publication No. 49027/1977 (this Japanese Patent application being based on German Patent application DT-AS No. 25 37 482 of Werner Holle).
When the above described visual indicator is employed, the photographer has to alternately change his sight between the image viewed through the viewfinder and the sign on the indicator during the lens adjustment, making the adjusting operation more difficult. Furthermore, the photographer may loose the decisive moment, as he has been occupied by the adjusting operation.